NSF PR 00-28 - May 4, 2000
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High Technology Meets the High Plains in STEPS-2000
Those tapered, bell-shaped thunderstorms that grace
so many calendars and posters aren't just photogenic,
they're a scientific mystery. Photographers love these
so-called low precipitation (LP) supercells because
of their spectacular cloud formations and sparse rainfall.
Yet researchers have generally ignored them: they
seldom produce tornadoes or flooding, and they tend
to occur across the High Plains instead of over more
densely populated areas.
Scientists are now realizing that the unsung LP storm
may hold a key to understanding the microphysics and
electrification of other kinds of thunderstorms. That's
why a group of researchers will set up shop in northwest
Kansas and eastern Colorado for the Severe Thunderstorm
Electrification and Precipitation Study (STEPS), funded
in part by the National Science Foundation (NSF).
Based in Goodland, Kansas, STEPS-2000 will take place
between May 22 and July 15. Involved organizations
include the National Center for Atmospheric Research
(NCAR) in Boulder, Colorado. NSF is NCAR's primary
sponsor. NSF will support a STEPS radar system operated
by Colorado State University and an airplane used
for microphysical and electrical measurements in thunderstorms,
operated by the South Dakota School of Mines and Technology,
serving as national facilities for the study.
"This is our first opportunity to bring together several
new techniques for observing the electrical properties
of storms and the rain and hail they produce," says
Rod Rogers, program officer in NSF's division of atmospheric
sciences, which funds STEPS2000. "We are expecting
a greatly improved understanding of the relationships
between thunderstorm electrification and precipitation
production -- and maybe some surprises."
STEPS-2000 will be the largest research effort to date
focused on lightning. Data from a national network
that tracks the location of cloud-to-ground strikes
has hinted at intriguing evolutions in lightning behavior
over the course of a storm. The STEPS-2000 study area,
along the semipermanent dry line that marks the west
edge of Tornado Alley, has one of the nation's highest
frequencies of lightning flashes. If STEPS-2000 can
follow a storm as it produces a tornado, the link
between a storm's electrical behavior and microphysics
should become more clear, say atmospheric scientists.
"We're particularly interested in lightning-free holes
in supercells," says William Rison, an New Mexico
Institute of Mining and Technology (NMIMT) electrical
engineer. NMIMT is also involved in STEPS-2000. A
system developed by researchers at NMIMT tracked two
supercell storms that each had a lightning-free circle,
roughly five kilometers wide, within a doughnut-like
ring of lightning. One storm produced a tornado in
the vicinity of the lightning-free hole. "The hole
was almost certainly associated with a very strong
updraft in the storm," notes Paul Krehbiel and NMIMT
colleagues. At the crown of the updrafts (15-20 kilometers
high) in both storms, a separate concentration of
lightning was found--to the surprise of researchers.
NCAR scientists Morris Weisman and Charles Knight are
especially interested in how embryonic storms become
LPs instead of taking a different route. "In the back
of everybody's mind, this has been a continuing mystery,"
said Weisman. Right now, he said, "The distinction
between HP [high-precipitation] and LP storms is largely
a visible one. Very often an LP will look weak on
radar, but if you're watching it in person you see
a tremendous updraft."
Another basic question is why the LP storms don't
produce much rain. They may contain as much water
vapor as their wetter counterparts, but they are far
less efficient at producing precipitation. Scientists
also don't know how these storms evolve into larger
storm systems later on.
Other agencies and institutions involved in STEPS-2000
include the National Weather Service, NOAA's National
Severe Storms Laboratory, the University of Oklahoma,
and FMA Research, Inc.
NSF is an independent federal agency which supports
fundamental research and education across all fields
of science and engineering, with an annual budget
of about $4 billion. NSF funds reach all 50 states,
through grants to about 1,600 universities and institutions
nationwide. Each year, NSF receives about 30,000 competitive
requests for funding, and makes about 10,000 new funding
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